1. Field of Invention
This invention relates generally to the field of ratcheting fastening devices and methods of use, more particularly, to shortening the locking distance of ratcheting fasteners by using double or multiple threads on one or more movable nut segments of the fastening device.
2. Description of Prior Art
A ratcheting fastener is a device that fastens to the external, threaded surface of a threaded rod. Such a device is capable of moving along the threaded rod in one direction, the “ratcheting direction” without rotation, but must be rotated in order to move along the threaded rod in the opposite “non-ratcheting” direction. Such devices are also called “ratcheting thread clamping devices” or simply “thread clamping devices” TCDs, which will be the designation used herein.
TCDs typically include a plurality of segments in a configuration so as to encompass some or all of the outer circumference of a threaded rod. The inner surfaces of some or all of the segments are threaded so as to engage with the threads of the threaded rod. The segments, or nut segments, are in a movable configuration (“movable nut segments”) so as to allow disengagement of the TCD with the threads of the rod when moved in the ratcheting direction, but do not disengage and must be rotated in the manner of a conventional nut in order to move in the opposite non-ratcheting direction.
Numerous examples of TCDs exist including the following: U.S. Pat. Nos. 5,081,811; 6,007,284; 3,695,139; 4,378,187; 4,974,888; 5,324,150; 5,427,488; 5,733,084; 5,988,965; 6,361,260; 6,406,240. While conventional TCDs use segments having frustoconical segments, recent work by the present inventor describes TCDs having segments with flat, not frustoconical, surfaces. These include embodiments described in U.S. Pat. No. 8,257,004 and pending U.S. patent application Ser. No. 13/385,135 (Patent Application Publication US 2012/0134764 A1, “'764”). The entire contents of these references are included herein by reference for all purposes.
For motion in the ratcheting direction, the one or more threaded segments engaging with the threads of the threaded rod disengage from one thread of the rod, slide over the thread to re-engage with the adjacent thread of the rod. The distance moved by the TCD in disengaging with one thread and engaging with the next thread is the “locking distance.”
In conventional TCDs, the threaded segments engaging the threads of the threaded rod have the same pitch as the threads on the rod. Thus, the locking distance is substantially the same as the thread pitch of the threaded rod.
However, there are important applications for TCDs, particularly in the construction industry, in which reducing the locking distance for a TCD engaging a threaded rod offers significant advantages.
For example, wood is a major construction material in many places throughout the world. Wooden structures frequently use “tie-downs” to secure the wooden structure to its foundation, typically a concrete foundation or a concrete and block foundation. The function of tie-downs is thus to secure the wooden structure to its foundation in the presence of forces (perhaps substantial forces) tending to separate the structure from its foundation, such as high winds, floods, seismic events, or general shifting and settling of the surrounding earth. However, the wood typically used for construction often has considerable water content when initially installed and with time, the water evaporates and the wood dries out. In the process of drying out, the wood dimensionally shrinks. Approximately 4% shrinkage in the first year following construction of a wooden structure is not uncommon. This shrinkage commonly causes tie-downs to loosen, thereby making the structure more susceptible to damaging displacements in the presence of high winds, earthquakes among other external forces. Catastrophic damage may result.
A common method for implementing a tie-down is by imbedding a vertical threaded rod into the concrete of the foundation at the location where the wooden structure is to be joined to the foundation. The threaded rod generally resides within the walls of a single or multilevel structure as it passes from the concrete foundation up through each floor of the structure. Each floor is typically attached to the threaded rod by a separate tie-down. The primary fastener presently used to implement a tie-down is a standard “hex” nut.
If a standard nut is used, a space will typically develop under the standard nut and above the wood as the wood shrinks in dimension due to loss of water as described above. This space allows the tie-down (and structure) to move vertically when an overturning moment is applied to the structure as might occur, for example, during a seismic event, wind loading, among other circumstances. This motion of the structure with respect to the foundation, in turn, allows for deformation of the structural walls and may produce substantial damage that the tie-down is designed to prevent when functioning properly, that is when holding the structure securely in place on the foundation. Thus, a need exists in the art for a tie-down that is self-compensating, that is, a tie-down that maintains secure attachment of the structure to the foundation despite shrinkage of the wood.
Two important facts and conclusions are apparent from the above statement of this important engineering and economic problem. First, a ratcheting tie-down device will ratchet to a lower position, thereby more firmly anchoring the structure, when there is sufficient shrinkage to permit ratcheting to the next thread position. That is, ratcheting occurs when the shrinkage is approximately the same as the locking distance. Therefore, decreasing locking distance in a ratcheting tie-down device leads to ratcheting with less shrinkage thereby increasing structural stability. Secondly, it would require a substantial change in structural design and construction procedures to alter the threaded rods to which tie-down devices attach, a serious barrier to adoption of different threaded rods. Therefore, it would be advantageous to achieve shorter locking distance by means of an improved TCD that requires no changes to the threaded rod(s) customarily used in the construction industry. The description of such a TCD is one objective of the present disclosure along with our co-pending application Ser. No. 12/309,574.
In fact, the importance of locking distance in maintaining structural stability is sufficiently great that the International Codes Council (“ICC”) has recently promulgated standards for locking distance that must be met for a device in order to achieve Code approval. The ICC has adopted Acceptance Criteria (“AC”), AC316, that require Tension Controlled Shrinkage Compensation Devices (“TCSCD”) to meet certain performance criteria. Among these is a requirement that the deflection of the TCSCD under load is limited to 0.125 inch minus “looseness.” “Looseness” as used in AC316 is defined as the distance the threaded rod must be moved in the locking direction relative to the TCD before the TCD segments lock to the rod. That is, ICC “looseness” is “locking distance” as used herein while “locking direction” equates with “ratcheting direction” as used herein.
Receiving formal ICC approval for a device is an important commercial advantage in the US market. But ICC approval is based upon successfully passing independent performance tests and evaluations, providing strong evidence of the devices' capabilities, even in those jurisdictions in which formal ICC approval is not a legal requirement. Thus, a need exists in the art for a TCD meeting ICC ACs, and also demonstrating improved overall performance.
It is expected that tie-downs and shrinkage-compensation devices as used in the construction industry are likely to be an immediate and important application for the structures and devices described herein. However, the present disclosure is not so limited and provides reduced locking distances for all manner of TCDs including those employing frustoconical or flat surfaces and for any field of use in which TCDs may be employed. Thus, a need exists in the art for structures and devices for reducing locking distances in ratcheting devices.